1. Field of the Invention
This invention relates to the preparation of polyester polyols from polycarboxylic and polyol components utilizing at least one polyol having both primary and secondary hydroxyl groups for property enhancement. The polyols are useful in the preparation of cellular foam materials, particularly polyisocyanurate and polyurethane foams.
2. Description of the Prior Art
The preparation of foams characterized by isocyanurate and urethane linkages is well known in the art. Generally, these foams are prepared by reacting an organic polyisocyanate with a polyol in the presence of a blowing agent and a catalyst(s). Polyester polyols of many types can be used as the polyol components in the production of these foams.
Because of the relatively high cost of typical polyols useful in making cellular polymers and because an inexpensive source of polyols is now available through the use of waste or scrap materials containing phthalic acid residues, efforts have heretofore been directed to processes for converting these materials to commercially useful polyester polyols. One such process is described in U.S. Pat. No. 3,647,759 and concerns transesterifying dimethyl terephthalate (DMT) process residue with ethylene glycol to form polyol reactants for reaction with polyisocyanate material in the production of polyurethane foams. The transesterification products of DMT process residue with ethylene glycol are unfortunately normally solid or balsamic, have limited compatibility with Freon 11 (trichlorofluoromethane blowing agent) and cannot be used as the sole polyol in Freon-blown foam systems unless special measures are taken to enhance their compatibility, such as the co-use of various compatibilizing agents.
U.S. Pat. No. 4,237,238 describes improved polyisocyanurate foam characterized by a high degree of fire resistance with low smoke evolution on combustion and low foam friability. The foam is obtained by bringing together in the presence of a blowing agent and trimerization catalyst an organic polyisocyanate and a polyol mixture prepared by the transesterification, with a glycol of molecular weight from about 60 to about 400, of the DMT process residue described in U.S. Pat. No. 3,647,759. Polyol mixtures of this type are available commercially from Hercules, Inc., Wilmington, Del. under the trade name Terate.RTM. Resins. Unfortunately, it has been determined that these commercially available polyester polyols of U.S. Pat. No. 4,237,238 which are derived by transesterifying the residue with excess diethylene glycol also have poor compatibility with the fluorocarbon blowing agents.
Further, U.S. Pat. No. 4,346,229 describes how liquid aromatic polyester polyols having excellent shelf stability and compatibility with trichlorofluoromethane can be produced by reacting DMT process residue with an excess of dipropylene glycol. However, various deficiencies have been encountered in producing and employing these polyester polyols. The reactions by which they're produced are undesirably long and give a by-product which reduces overall yield. The polyols also have an excessively high viscosity and their use in various foam formulations results in unduly extended reactivity profiles.
Thus, there still is a need in the art for a polyester polyol which does not have the aforementioned disadvantages.